1. Field of the Invention
This invention relates to printing devices of the "stored energy" type in which a flexible hammer element carrying an impact tip is flexed to a cocked position by means of a permanent magnet. A coil is employed to generate an electromagnetic field which overcomes the magnetic field of the permanent magnet thereby releasing the hammer element and enabling it to fly forward toward an impact position. More particularly, the present invention is directed to a dot matrix actuator in which a plurality of hammer elements are employed to print dots to form characters. Still more particularly, the present invention relates to a dot matrix actuator in which flat spring magnetic hammer elements are employed in connection with a magnetic circuit containing at least one pole element, a permanent magnet coupled to the pole element and a coil surrounding the pole element.
2. Description of the Prior Art
Stored energy type print actuators are well known in the art. Actuators of this type are disclosed in the following U.S. Pat. Nos. 3,804,009 to Blume; 3,842,737 to Gomi; 3,941,051 to Barrus, et al.; 4,033,255 to Kleist, et al.; 4,044,668 to Barrus, et al.; 4,233,894 to Barrus, et al.; 4,258,623 to Barrus, et al.; and 4,280,404 to Barrus, et al. The '894 and '623 patents to Barrus, et al. disclose print hammer mechanisms which incorporate dual pole pieces. In both of these patents, when the spring hammer is in the retracted position, it contacts only one of the poles and a gap is maintained with the second pole. The gap is employed to improve the hammer release and retract capabilities.
All of the above patents disclose a print mechanism having a single row of printing elements whose impact tips are arranged along a print line. Printing is accomplished by successively printing rows of the character matrix and advancing the printing medium between the printing of each row of dots. This printing technique places several demands upon the precision of the shuttle mechanism which moves the actuators.
Dot matrix printers have been developed in which printing elements are arranged vertically so that an entire character is printed with each pass of the actuator. Such systems are disclosed in U.S. Pat. Nos. 3,999,644 to Pape, et al.; 4,136,978 to Bellinger, Jr., et al.; and 4,278,020 to Oaten. In the Pape and Oaten patents, the actuators are arranged so that the impact points lie along a line which is slanted with respect to the printing line. Neither of those patents is directed to a stored energy type actuator.